652 
Journal of Agricultural Research 
Vol. XXIII, No 8 
Table IV. Effect of formaldehyde on sclerotia and mycelium buried at different depths 
in soil 
Part of fungus treated. 
Viable, 
sur¬ 
face. 
Viable, 
. 4 
inches. 
Viable, 
8 
inches. 
Viable, 
12 
inches. 
Viable, 
16 
inches. 
Viable, 
20 
inches. 
Moisture 
condition 
when buried. 
0 
O 
O 
0 
0 
0 
Sclerotia from lettuce plants 
O 
0 
0 
0 
O 
O 
0 
O 
0 
O 
which showed first symp- 
0 
0 
0 
0 
0 
0 
toms of drop 8 days before 
0 
0 
O 
0 
Q 
>Moist. 
sclerotia were treated. 
0 
0 
O 
0 
O 
O 
0 
0 
O 
2 
O 
0 
0 
0 
O 
1 
O 
O 
Sclerotia from infected lettuce 
plants. 
0 
0 
0 
0 
O 
0 
1 
2 
O 
5 
0 
1 
3 
4 
0 
3 
0 
2 
Sclerotia 
air-dried 
for 15 
Sclerotia from pure culture 
0 
0 
O 
2 
0 
2 
days. 
19 days. 
Sclerotia from pure culture 
0 
0 
O 
2 
8 
e 
20 days. 
White mycelium from surface 
0 
0 
O 
0 
1 
O 
^oist. 
of infected lettuce plants. 
Mycelium in decomposing let¬ 
O 
O 
O 
0 
0 
O 
tuce leaves. 
4 
As previously stated, the moisture content of sclerotia at the time of 
treatment is a very important factor in killing sclerotia with formal¬ 
dehyde. This is again made evident in Table IV by comparing the 
effect of treatment on sclerotia in which a moisture content was main¬ 
tained by contact with the host plant, and on air-dried sclerotia. In 
eight trials where sclerotia were removed directly from the host and 
treated, six showed all sclerotia killed down to 20 inches. In the other 
two trials the treatment was effective at a maximum depth of 12 inches. 
Sclerotia air-dried for 15 days were killed at a depth of 4 to 8 inches. 
Sclerotia taken from pure culture and treated in the same matmer were 
apparently about as resistant to the action of formaldehyde solutions in 
the soil as sclerotia taken from lettuce plants. Obstructions in the soil 
such as pebbles, rocks, dry earth, etc., may act as shields preventing the 
formaldehyde from reaching the fungus, which possibly explains the 
variations in results. 
A sclerotium has been defined as “ a compact mass of hyphae in dor¬ 
mant state.” The compactness of the dormant hyphae and the thick 
walls of the cells makes it extremely difficult for most disinfectants to 
penetrate to the interior cells of a sclerotium. Although formaldehyde 
is very penetrating it failed to kill the sclerotial stage of the fungus as 
quickly as the vegetative stage under the same conditions (Table IV). 
TREATMENT OF GREENHOUSE SOILS FOR THE CONTROL OF S* 
LIBERTIANA 
Since laboratory tests with formaldehyde proved so effective against 
the sclerotia and mycelium of 5 . libertiana it seemed advisable to test 
thoroughly its value for the control of this fungus as it occurs naturally 
in greenhouse lettuce soils. Therefore, extensive experiments have been 
